Lubricity reduces the friction that is inevitably generated between two faces that relatively move at the time of transfer of force or change of direction due to mechanical mechanism. In order to improve this lubricity, a lubricity improver is used at most facilities where the mechanical mechanism occurs, and thus, the lifespan of a machine can be extended, resulting in increasing production activity. Meanwhile, since a high-pressure ignition type diesel engine as well as the machine requires lubricity of fuel, a lubricity improver is mixed in the fuel at a predetermined mixture ratio in order to secure lubricity of the fuel for diesel engine.
The lubricity improver may be largely classified into inorganic compounds, metals, and organic compounds. There are polymers, synthetic lubricant from metal oil, and the like. Recently, a vegetable lubricant has been increasingly used as an ecofriendly lubricant. In the vegetable lubricant, fatty acid methyl ester obtained from animal or vegetable oil has been known to have excellent lubricity.
U.S. Pat. No. 4,609,376 discloses, as a lubricity improving additive for alkanol fuel, ester of monovalent or polyvalent carboxylic acid and polyvalent alcohol (but, having at least two free hydroxy groups).
EP 0635,558 and EP 0605,857 disclose, as a lubricity improving additive of diesel fuel, vegetable oil such as rap seed oil, line seed oil, soya oil, canola oil, or sunflower oil, and ester of the vegetable oil.
Korean Patent Laid-Open Publication No. 10-2005-0052460 discloses, as a lubricity improving additive having improved low-temperature characteristics, a fatty acid composition having saturated fatty acid and unsaturated fatty acid, where fatty acids having different chain lengths are specifically distributed and specifically contained.
Korean Patent Laid-Open Publication No. 10-1999-0043777 discloses, as a lubricity improving additive, purified fatty acid, an ester compound obtained by reacting fatty acid and an alcohol compound, or a mixture thereof.
Meanwhile, the unsaturated fatty acid methyl ester containing olefin (double bond) is in a liquid phase while the saturated fatty acid methyl ester is mostly in a solid phase, and thus, the unsaturated fatty acid methyl ester has known to have excellent lubricity as compared with the saturated fatty acid methyl ester. However, when the unsaturated fatty acid methyl ester is stored for a long time, the olefin in the molecule is easily oxidized, which is converted into an epoxy group, a monol compound, or a diol compound, thereby changing physical property and increasing the acid value. Resultantly, this fatty acid methyl ester has poor storage stability, and since the acid value of the fatty acid methyl ester is increased at the time of storage thereof, it may corrode metals.
The corrosion of metals due to oxidation of the lubricity improver may accelerate mechanical friction and wear, resulting in deteriorating the condition of a machine.
That is, the lubricity improver needs to be in a uniform liquid state while being mixed in the fuel, needs to have excellent oxidation stability and good storage stability, and needs to reduce the friction and wear of two faces by providing excellent lubricity.
Although many studies on the existing fatty acid methyl ester type lubricity improver have been reported, there is no study that lubricity is improved and storage stability due to anti-oxidation is improved by substituting olefin in the fatty acid methyl ester with another functional group.
Therefore, in order to make up for the deficiencies of the existing fatty acid methyl ester type lubricity improver and improve the lubricity more effectively, a new type lubricity improver needs to be developed.